Photographic film-handling appliance

ABSTRACT

An electric motor is energizable to rotate a rotary shutter. A release switch is movable between an operative position and an inoperative position. A power supply circuit is adapted to energize the motor when the release switch is in the operative position. Electric braking means are energizable to stop the shutter. Fully electric brake control means are operatively connected to the shutter and arranged to de-energize the braking means when the release switch is in its operative position and to energize the braking means at least temporarily so as to stop the shutter in a predetermined position when the release switch has moved from its operative position to its inoperative position.

United States Patent [1 1 Drasch et al.

[4 1 May 14, 1974 [73] Assignees: Karl Vockenhuber; Raimund Hauser, bothof Vienna, Austria Filed: July 6, 1971 Appl. No.: 159,698

Foreign Application Priority Data July 6, 1970 Austria 6112/70References Cited UNITED STATES PATENTS 7/1942 Fuller t 1. 352/176 X8/1968 Schrader 352/179 X Int. Cl. G03b 1/00 1,880,106 9/1932 Robinson352/30 3,567,316 3/1971 Wilharm 352/178 X FOREIGN PATENTS 0RAPPLICATIONS 1,120,101 7/1968 Great Britain... 352/174 U.S.S.R 1.352/176 Primary ExaminerMonroe H. Hayes 5 7] ABSTRACT An electric motoris energizable to rotate a rotary shutter. A release switch is movablebetween an operative position and an inoperative position. A powersupply circuit is adapted to energize the motor when the release switchis in the operative position. Electric braking means are energizable tostop the shutter. Fully electric brake control means are operativelyconnected to the shutter and arranged to de-energize the braking meanswhen the release switch is in its operative position and to energize thebraking means at least temporarily so as to stop the shutter in apredetermined position when the release switch has moved from itsoperative position to its inoperative position.

10 Claims, 12 Drawing Figures 1 PHOTOGRAPHIC FILM-HANDLING APPLIANCEThis invention relates to a photographic or cinematographic recording orreproducing appliance, preferably a motion picture camera, whichcomprises an electric motor for driving a shutter, a release switchhaving an operative position, in which the electric motor is energized,and an inoperative position, in which the electric motor isde-energized, and exclusively electric means which are connected to therelease switch and serve to arrest the shutter in a predeterminedposition.

It is known that such appliances, particularly motion picture cameras,can be de-energized so that the shutter is in a desired position if astop is provided, which is moved into the path of a cooperating stopthat is connected to the drive means. To avoid a detrimental reaction onthe drive motor in such arrangements, the drive means may comprise anoverload coupling. Such overload coupling in most cases requires a largespace and for this reason is inconsistent with a compact structure. Acamera is known which comprises an exclusively electric means forarresting the shutter in a predetermined position. In that camera, anoscillator operating at a variable frequency delivers pulses to a ringcounter, which orders said pulses to provide a phase voltage of athree-phase system. That phase voltage is amplified and then fed to arotating field induction motor having a magnetic rotor. A so-calledstarting storage device ensures that the motor is electrically stoppedalways at the same phase angle and started always with the same phase,which succeeds said phase angle. That design is mostexpensive and forthis reason cannot be used in appliances used by amateurs.

The invention eliminates these difficulties in that means are providedwhich are connected to the shutter and operated in dependence on theposition of the shutter and which in a manner known per se render aneddy current brake and/or counter-current brake operative at leasttemporarily and particularly short-circuit the motor. Said means arecontrolled by the releaseswitch in such a manner that the means areoperative when the release switch is in its inoperative position and themeans are inoperative when the release switch is in its operativeposition. Whereas cinematographic appliances are known which comprise aneddy current brake, said eddy current brake served only to control thespeed of the motor. it is also known to short-circuit the motor foroperating a zoom lens when the motor has been de-energized. According toa proposal which has not been disclosed in a printed publication, it hasalready been'attempted to short-circuit thedrive motor.

of a camera when the motor has been deenergized. That arrangement,however, does not provide for a proper synchronization with the positionof the shutter so that the need for mechanical means for stopping theshutter could not be eliminated.

In the simplest case, the eddy current brake may cooperate in knownmanner with a sector-shaped'conducting disc whereas the release switchconsists of a change-over switch. in this case, the release switchenergizes either the motor or the eddy current brake and the action ofthe eddy current brake is initiated when the shutter is in the desiredposition because the sectorshapcd'disc hasa corresponding configurationor the pole pieces of the eddy current brake have a corre spondingconfiguration. In this arrangement, a particularly good braking actionwill be obtained if the sectorshaped disc is driven by aspeed-increasing transmission. In this case, however, a plurality ofpole pieces of the eddy current brake in a numberwhich corresponds tothe transmission ratio must be spaced around the disc. It is simpler toprovide a rotary shutter disc consisting of a conducting disc. A furthersimplification may be obtained in that the winding of the eddy currentbrake is formed by the stator winding of the motor.

According to a preferred feature of the invention, at least one circuitis provided which by-passes the release switch and comprises a by-passswitch, which is adapted to be closed for a time which is shorter thanone cycle of the shutter, and said circuit comprises, if desired, aresistor for braking the motor. Said by-pass switch maybe connected tothe shutter responsive to the position thereof in such a manner that theby-pass switch is closed and the brake-actuating switch is open when theshutter has moved beyond its predetermined position, whereas the twoswitches are in their respective opposite positions before the shutterhas reached that predetermined position and, if desired, both switchesare open when the shutter is in its predetermined position. In order toprevent a movement of the shutter beyond its predetermined position whenthe release switch has been opened, it is a feature of the inventionthat the closing of the by-pass switch when the release switch is opencauses the motor to be reversed, e.g., by means of a reversing switchconnected to the release switch. Particularly when electronic switchingcircuits are used, the by-pass switch consists preferably of aphotodetector, e.g., a photodiode, which is illuminated in dependence onthe position of the shutter.

In an arrangement according to the invention, a special problem residesin the provision for single frame operation. For this purpose, theabove-mentioned bypass switch or an additional by-pass switch may bedesirable if the single frame operation is enabled by means for closingthe by-pass switch or another switch which bypasses the release switchand is adapted to be closed for a short time. In such arrangement, thebypass switch controlled by the shutter may be supplemented by apulse-generating switch, which may be operated to supply a current pulseto the motor. In many known cameras and also in projectors, a modecontrol switch for changing between continuous operation and singleframe operation is provided. In such arrangement, the release switchitself may consist of a pulse generating switch and the mode controlswitch may be connected to means for holding the motor circuit closedwhen the release switch is closed for continuous operation. This conceptmay be realized in various ways. For instance, the means connected tothe mode control switch maybe formed by a locking device, which holdsthe pulse-generating switch in its unstable position. lna preferredarrangement, however, the release switch when closed is connected to acontact that is included in the circuit of an interrupter that iscontrolled by the mode control switch. Alternatively, said by-passswitch may be closed in that a starting device is provided, which servesto mechanically rotate the drive means until the by-pass switch has beenclosed.

In cameras having a circuit which is adapted to be energized by a mainswitch, the arrangement according to the invention affords the specialadvantage that there is no need for additional means which prevent aninadvertent opening of the main switch when the release switch isclosed. This object will be accomplished if the main switch, which ispreferably arranged to be closed by the inserted film cartridge, isconnected between the power source and the release switch because inthat case the by-pass switch ensures that the shutter will assume itspredetermined position in any case before or after the release switchhas returned to its opened position, even when the main switch is open.When the film cartridge has been removed, the presence of the bypassswitch which might prevent a permanent deenergization of the motor whenit has run up because the load on the drive means is reduced and theby-pass switch iscontinually closed. This phenomenon will be preventedif the main switch is arranged to be closed by the insertion of the filmcartridge.

Electronic components may be used to advantage in an arrangementaccording to the invention. For instance, the pulse-generating switchfor single frame operation may be formed by a 'monostable multivibratorstage, which is adapted to be driven by a time constant circuit. One ofthe transistors of such multivibrator stage may serve as a switchingtransistor for the motor. In this case, a preferred feature-resides inthat this switching transistor may serve at the same time as a finalcontrol element of the speed control system for the motor, the switchfor controlling the brake may also consist of a transistor having anemitter-collector path which shunts the motor. In this way, at leastpart of'the switching circuits may easily be made as integratedcircuits. v

Further details of the invention will become apparent from the followingdescription of embodiments which are shown diagrammatically and by wayof example in the drawings, in which FIG. I is a sectional view showinga camera according to the invention,

FIG. 2 is a sectional view taken on line IIlI in FIG.

FIG. 3 is a diagrammatic representation of a simplified embodiment ofthe invention,

FIG. 4 is a sectional view which is similar to FIG. 1 and shows a detailof another embodiment,

FIG. 5 is a diagrammatic representation of a further embodiment, I

FIGS. 6 to 9 show various positions of a further embodimen't,

FIGS. 10, 11 are circuit diagrams of two embodiments of means forenabling single frame operation, and

FIG. 12 shows an embodiment of an arrangement according to the inventionwhich is composed of electronic components.

A camera 1 provides a light path from a diagrammatically indicated lens2 through a rotary shutter 3 and an exposing aperture 4 to a film 5,which is disposed be hind the exposing aperture 4. A pull-down claw 6 isprovided to move the film 5 and is driven by a pulldown cam 7. Thepull-down cam is mounted on the same shaft 8 as the rotary shutter 3.That shaft 8 carries also a gear 9, which is driven by 'a pinion mountedon the shaft of a motor 11. The shaft 8 is mounted at one end on theplate 12 which defines the exposing aperture 4 and at the other end onanother plate 13. The plate I3 carries a printed circuit, whichcomprises slip rings that cooperate with sliding contacts l4, 15 on thegear Wheel 9. A microswitch 16 is soldered to the plate 13. Thatmicroswitch 16 consists of a change-over switch and forms the releaseswitch of the camera 1. The release switch 16 is operable by a releasemember 17 in such a manner that the movable contact 18 moves from aninoperative position, which is shown in FIG. I and in which the contact18 engages a normally closed contact 19, to its operative position, inwhich the movable contact 18 engages a normally open contact 20.

It is apparent from FIG. 2 that the sliding contacts l4. 15 areconductively interconnected. The contact I9 is engaged by the movablecontact 18 when the release switch 16 is in its inoperative position andis connected to an intermediate slip ring 21 on the plate 13. Themovable contact 18 is connected to a motor terminal 22, which isdirectly soldered to the printed circuit. The other motor terminal 23 isdirectly connected to one terminal of a power source 24 and is alsoconnected to an outer half-ring 25 on the plate 13. The half-ring 25 andanother half-ring 26 form together a complete ring. The half-ring 26 isconnected to the other terminal of the power source 24 and to thenormally open contact 20.

Upon an operation of the release member 17, the movable contact 18engages the normally open contact 20 so that the motor 11 having aterminal 23 connected to one terminal of the power source 24 is nowconnected by its terminal 22 and the contacts 18, 20, also to the otherterminal of the power source 24. When the release member 17 is thenreleased, the release switch 16 assumes is inoperative position, inwhich the movable contact 18 engages the normally closed contact 19.When the shutter 3 and with it the gear 9 carrying the sliding contactsl4, 15 are in the position shown in FIG. 2, the motr II isshort-circuited by the terminal 23 and by the half-ring 25, the twosliding contacts l5, 14, the slip ring 21, the contacts l9, l8, and theterminal 22 so that the motor is braked quickly. When the shutter 3 isin a position to expose the exposing aperture 4, the sliding contact 15engages the half-ring 26 to connect the latter through the slidingcontact 14 and the contacts 19, 18 to the motor terminal 22. Because themotor is connected by its terminal 23 to one terminal of the powersource 24 and is connected by its terminal 22, the contacts l8 19, theslip ring 21, the sliding contacts l5, l4 and the half-ring 26 to theother terminal of the power source 24, the energization of the motor 11is continued until the shutter 3 has rotated to its predeterminedposition, in which it is braked by the then short-circuited motor 11.Hence, the half-ring 26 and the sliding contacts 14, 15 form a by-passswitch for temporarily by-passing the release switch 16.

FIG. 3 shows that the invention may be embodied in much simplerarrangements. In FIG. 3, parts having the same function are designatedwith the same reference characters as in the preceding Figures. Therotary shutter 3 consists of a conducting disc, which cooperates with aneddy current brake 27. In this embodiment, the eddy current brake 27 isenergized as soon as the release switch 16 has moved to its inoperativeposition shown in FIG. 3. A braking action will not be exerted by theeddy current brake 27, however, until the conducting disc 3 movesbetween the pole pieces of the eddy current brake 27. Hence, there willbe no braking action as long as the shutter disc 3 exposes the exposingaperture 4 because the sector-shaped part of the disc 3 is not disposedbetween the pole pieces of the eddy current brake; these pole pieces aredisposed adjacent to the exposing aperture 4. The eddy current brake 27will not become effective until the shutter disc 3 assumes itspredetermined position, in which the disc 3 covers the exposing aperture4. It will depend substantially on the dimensioning of the eddy currentbrake 27 at what point of the path of the shutter disc 3 the eddycurrent brake is actually disposed. The braking action will be increasedif the eddy current brake cooperates with a sector-shaped disc which isdriven by a speedincreasing transmission. The design of the disc and ofthe eddy current brake will then be selected in view of the transmissionratio.

FIG. 4 shows an embodiment which enables a single frame operation. Allparts not required for an under standing of this embodiment have beenomitted in F IG.; 4. In the embodiment of FIG. 4, the release member 17operates the movable contact 18 of the switch 16 by a slider 28 ratherthan directly. The latter comprises slots 29, 30, which are passedthrough by stationary pins.31, 32. The release member 17 comprises twonipples 33, 34 for the connection ofa cable release. The nipple 33 isused for continuous operation and the nipple 34 for single frameoperation. The nipple 33 is in register with the slider 35, which isalso guided by the pins 31, 32 but has a much larger opening 36 adjacentto the pin 32. The slider 35 is formed with a shoulder 37, which isengaged by an extension 38 of the slider 28 under the actionof a coiledtorsion spring 39. The other end portion of the spring 39 directlyengages the slider 35.

When a cable release screwed into the nipple 34 is operated to push theslider 35 to the right of FIG. 4,.the movement of the slider 35 istransmitted by the shoulder 37 and the extension 38 to the slider 28.The latter moves the movable contact 18 of the switch 16 into engagementwith the normally open contact 20. At the same time, an extension 40 ofthe slider 35 is moved into the path of a hook 4-1, which is connectedto the pulldown claw 6 and which engages the extension 40 during theupward movement of the pull-down claw 6. The enlarged opening 36 permitsthe slider 35 to follow the movement of the pull-down claw 6 to itsupper dead center. so that the slider 35 is pivotally moved about thepin 31. That pivotal movement causes the shoulder 37 to disengage theextension 38 so that the spring 39 causes the slider 28 to return to itsleft-hand end position so as to return the release switch 16 to itsinoperative position.

FIG. 5 shows a slip ring half 42, which is connected to the shutter 3and cooperates with stationary sliding contacts 43 to 46. The slidingcontacts 43, 44 are connected to respective terminals of the powersource 24. The sliding contacts 45, 46 are connected one to the other.

When the release switch 16 is in its operative position, the motor 11 isdirectly connected to the power source 24. When the release switch 16 isin its inoperative position, shown on the drawing, and the half-ring 42connected to the shutter 3 connects the sliding contacts 44, 46, themotor 11 is short-circuited by its terminal23 and by the slidingcontacts 44, 46, the contacts 18, I9, and the terminal 22. When theshutter 3 is in the position in which the exposing aperture 4'isexposed, the half-ring 42 connects the sliding contacts 43, 45 so thatthe normally open contact of the release switch 16 is bypassed becausethe terminal 22 of the motor 11 is then connected to one terminal of thepower source 24 through the contacts 18, 19 and the sliding contacts 43,45.

According to FIG. 5, the power source 24 feeds the motor circuit and anexposure control circuit 47. As in numerous known appliances. a mainswitch 48 is provided to prevent a flow of current through the exposurecontrol circuit 47 when the appliance is inoperative. Previously,mechanical locking means were required to prevent'an inadvertent openingof the main switch of the appliance while the motor was running becausesuch opening would cause the shutter to stop in an uncontrolled positionso that an ingress of light into the film cartridge could not beprevented. That problem maybe solved with simpler means in that the mainswitch 48 is included in the circuit which is by-passed by the circuitincluding the by-pass switch 43, 45 so that even when the main switch 48is opened inadvertently, the shutter 3 can still move to itspredetermined position, in which the shutter 3 covers the exposingaperture 4.

Another embodiment which enables a single frame operation is shown inFIG. 5. In this embodiment, the contacts 43, 45 are connected toenergize the motor 11 so that the movement of the shutter 3 is continuedfor one revolution. A mechanical starting device is provided to connectthe contacts 43, 45. That device comprises a slider 50, which is biasedby a spring 49 and guided by a pin 52, which extends through a slot 51,and by a guide pin 53. A pawl 54 is provided at one end of the slider 50and can cooperate with a ratchet wheel 55, which is secured to the shaft8. For this purpose, the slider 50 is moved in the direction of thearrow E by a cable release, not shown, against the action of the spring49, so that the pawl 54 engages the ratchet wheel 55 and rotates thesame together with the shutter 3 until the slip ring 42 connects thecontacts 43, 45. The motor 11 is now enrgized and the shutter 3 isdriven until the motor 11 is again short-circuited by the contacts 44,46 so that the shutter 3 is stopped in a predetermined position.

. In order to prevent a continual movement of the shutter beyond itspredetermined position when the load on the drive means is insufficientso that the bypass switch continually turns on the motor 11, means forenergizing an eddy current brake may be provided. Such means are shownin FIGS. 6 to 9. In the embodiment shown by way of example, the shutter3 is provided with four sliding contacts 56, 57 and 58, 59, which may beconnected in pairs like the sliding contacts 14,15 in FIGS. 1 and 2.These sliding contacts 56 to 59 cooperate with sliding contacts whichare carried by a plate, not shown, and which have the same form as theillustrated sliding contacts. That plate which is not shown is similarto the plate 13 shown in FIGS. 1 and 2. A release switch 60 comprisestwo movable contacts 61, 62, which are connected to respective terminalsof the voltage source. When the release switch 60 is in its inoperativeposition, shown in FIGS. 6 to 9, the center contacts 61, 62 areconnected to stationary contacts 63, 64. The contact 63 is connected tothe left-hand, outer slip ring 65. A further quadrant arc 65a is coupledby a braking resistor 66 to the slip ring 65. The remainingouter'quadrant and three quadrants of the adjacent inner slip ring areconnected to the negative terminal of the power source by the contacts64, 62. The two terminals 22, 23 of the motor 11 are soldered torespective additional inner slip rings 68 and 69, and when thereleaseswitch is in operative position are directly connected bystationary contacts 70, 71 to the two terminals of the voltage source.Since current flows through the slip rings 68, 69, the sliding contacts56'to 59 and the remaining slip rings when the release switch is in itsoperative position, there will be no effeet, particularly because the.connection to the contacts 63, 64is interrupted. When the release switch60 and the shutter 3' are in their inoperative position, shown in FIG.6, the sliding contacts 56 and 59 are insulated from thecurrent-carrying slip rings 65 and 67, respectively so that the motor llis at rest.

When the release switch 60 has returned from its operative position toits inoperative position, the contacts 70, 71 will be by-passed when theshutter disc 3' is in a position shown in FIG. 7. For this reason, thefull energization of the motor 11 is continued through the contacts 61,63, the slip ring 65, the sliding contacts 59, 58 and the slip ring 68,on the one hand, and through the contacts 62, 64, the slip ring 67, thesliding contacts 56, 57 and the slip ring 69, on the other hand. Thecurrent thus supplied will be reduced as soon as the shutter disc 3assumes the position shown in FIG. 8 because the sliding contact 59 thenslides on the quadrant arc 65a, which is connected to thecurrent-carrying slip ring 65 by the braking resistor 66. This willprepare the braking of the motor 11. Within the scope of the invention,the'slip rings might be designed and connected so that the braking isinitiated by a short-circuiting of the motor 11.

Owing to its flywheel effect, the shutter disc 3' having left thequadrant arc 65a obviously will not stop in its inoperative positionshown in FIG. 6 but will move to a position such as shown in FIG. 9,lll'.WlllCh a reverse current flows through the motor 11 because thesliding contact 59, which previously cooperated with the slip ring 65,65a connected to the positive terminal of the power source now contactsthe slip ring 67, which is connected to the negative terminal of thevoltage source. At the same time, the sliding contact 56 has moved fromthe slip ring 67 to the slip ring 65 so that the motor 11 is suppliedwith reverse current. As a result. the shutter disc 3' is first brakedand then returned to its inoperative position shown in FIG. 6. There maybe a slight hunting until the shutter disc 3 finally remains in itspredetermined position. That hunting is damped particularly because onlya low current flows through the quadrant arc 65a.

FIGS. 4 and 5 show embodiments which enable a single frame operation.Modifications of these embodiments are shown in FIGS. 10 and 11. Aswitchgear block 72 represents the bypass switch and the braking switch,which may be designed as shown in FIG. 5, for instance. in bothmodifications, means are provided which cause the shutter disc to rotatethrough a small angle until the by-pass switch is closed. That smallrotation of the shutter disc is effected in. both embodiments by a shortcurrent pulse.

According to FIG. 10, the circuit of the motor 11 includes a releaseswitch 73 and a single frame switch 75, which is operable by a singleframe release 74. The single .frame switch consists of apulse-generating switch and has two inoperative positions, in which themovable contact member 76 of the switch engages stops 77 and 78,respectively. The operation of the single frame release 74 causes themovable-contact member 76 to move from one inoperative position to theother. During this movement the contact member 76 is in contact for ashort time with a stationary contact strip 79. The

length of the Contact strip 79 is sufficient to ensure that the by-passswitch cooperating with the rotary shutter will be reliably closedduring the pivotal movement of the contact member 76.

Cinematographic appliances are often provided with a mode controlswitch, which may be set to positions for continuous operation and forsingle frame operation. In the embodiment shown in FIG. 1], such modecontrol switch may be connected to a switch 80 for a change betweencontinuous operation and single frame operation. The switch 80 may beopened for a taking or reproduction of single frames and closed forcontinuous operation. Regardless of the position of the switch 80, themotor ll is always started by the operation of a release 81, whichcooperates with a release switch 82, which consists of apulse-generatingswitch. When the release switch 82 is in its operativeposition, the movable contact member 83 contacts a stationary contact84, which corresponds to the normally closed contact 19 of the releaseswitch 16. Another stationary contact 85 in the circuit of the switch 80corresponds to the normally open contact 20 of the release switch 16. Acontact strip 86, which corresponds to the contact 79 (FIG. 10) isdisposed between the two contacts 84, 85.

When the switch 80 has been opened to set the appliance for single frameoperation and the release member 81 is operated so that the contactmember 83 slides over the contact strip 86, a switch 87 disposed behindthe contact strip 86 will be opened at the same time. The movablecontact member 83 finally engages the stationary contact 85, which is incircuit with the open switch 80. During the movement of the contactmember 83 in contact with the contact strip 86, the motor 11 has movedthrough an angle which is just sufficient to cause the closing oftheby-pass switch, which cooperates with the shutter. As a result, themotor 11 is braked after one revolution. When the contact member 83 isreturnd toward the normally closed contact 84, the contact member 83again slides on the contact strip 86. Because the switch 87 has beenopened during the release, the motor 11 remains de-energized and thecontact member 83 returns to its inoperative position while closing theswitch 87.

FIG. 12 shows how the invention can easily be realized by' means ofintegrated switching circuits. The switching elements for switching themotor 11 comprise a single frame switch 88, a release switch 89, abypass switch 90 consisting of a photodetector, a monostablemultivibrator comprising two transistors 91 and 92, and anothertransistor 93. One transistor 92 of the multivibrator serves as aswitching transistor for the motor 11 and conducts only when one of theswitches 88, 89, and 90 is closed. For instance, when the release switch89 is closed, the switching transistor 92 conducts so that the motor 11is in normal operation. A speed control circuit 94 may have an outputwhich is connected to the base of the switching transistor 92 so thatthe latter serves also as a final control element of the speed controlsystem. The shutter disc may be or may not be in its predeterminedposition before the exposing aperture when the release switch 89 isopened. This is detected by the photodetector 90, which is disposedbehind the rotary shutter adjacent to the exposing aperture or receiveslight from the light-reflecting surface of the shutter disc. Unless theshutter disc covers the exposing aperture, the photodetector 90 isilluminated and constitutes a closed by-pass switch so that theswitching transistor 92 remains conducting. As soon as the illuminationof the photodetector 90 ceases, the switching transistor 92 is blockedand the transistor 91 is rendered conducting as well as the transistor93. Because the emitter-collector path of the transistor 93 shunts themotor 11 and thus connects the two terminals of the motor 11, the latteris braked.

To enable a single frame operation, a capacitor 95 is provided as wellas a time constant circuit including a capacitor 96. The capacitor 95 isin circuit with the single frame switch 88. When the latter is closed,the ca pacitor 95 is closed. During the charging of the capacitor 95,the capacitor 96 is charged too. During that time, the switchingtransistor 92 is rendered conducting for a short time. This issufficient for an angular movement of the shutter disc until thephotodetector 90 is illuminated and holds the switching transistor 92con ducting until the shutter disc has returned to its prede terminedposition of rest, in which it is braked by the transistor 93 when thetransistor 92 has been blocked.

What is claimed is:

1. In a photographic film-handling appliance means defining an opticalpath,

a shutter arranged on said optical path and having an open'position anda closed position, i

an electric motor drivingly connected with said-shutter to control itsposition,

a power supply circuit to energize said motor,

a braking circuit including fully electric brake means to stop saidmotor,

release switch means having a first position for interrupting saidbraking circuit, and a second position for interrupting said powersupply circuit, v

a bypass circuit disposed to by-pass said release switch means in saidsecond position,

by-pass switch means arranged within said by-pass circuit and operatedby said motor, said by-pass switch means for interrupting said by-passcircuit in said'closed position of said shutter and being closed in saidopen position of said shutter,

braking switch means arranged within said braking circuit and operatedby said motor, said braking switch means for interrupting said brakingcircuit in said open position of said shutter and being closed in saidclosed position of said shutter,

said electric brake means for being energized only with said brakingswitch means being closed and with said release switch in'said secondposition.

2. The appliance, as set forth in claim 1, wherein said by-pass circuitincludes a braking resistor for said motor,

3. The appliance, as set forth in claim I, wherein said by-pass switchmeans comprise a photoelectric transducer and means for transmittinglight to said transducer only with saidshutter in open position.

4. The appliance, as set forth in claim 1, further comprising manuallyoperable means'to close forcibly said bypass switch means'for a periodcorresponding in a maximum to the period of said open position of saidshutter when said shutter is standing still in said closed position andsaid motor is de'energized.

5. The appliance, as set forth in claim 4, wherein Said manuallyoperable means comprise means to totate saidshutter until said by-passswitch means are closed.

6. The appliance. as set forth in claim I, wherein said release switchmeans comprise a release switch anda brake control switch. said switchesbeing operatively interconnected.

7. An appliance, as set forth inclaim 6, wherein said brake controlswitch means comprises a switching transistor having anemitter-collector path shunting said motor.

8. In a photographic film-handling appliance means defining an opticalpath,

a shutter arranged on said optical path and having an open position anda closed position,

an electric motor drivingly connected with said shutter to control itsposition,

a power supply circuit to energize said motor,

a braking circuit including fully electric brake means to stop saidmotor,

I release switch means having a first position for inter rupting saidbraking circuit, and a second position for interrupting said powersupply circuit,

7 a first by-pass circuit to by-pass said release switch means in saidsecond position,

first by-pass switch means arranged within said first by-pass circuitand operated by said motor, said first by-pass switch means forinterrupting said bypass circuit in said closed position of said shutterand being closed in said open position of said shutter,

braking switch means arranged within said braking circuit and operatedby said motor, said braking switch means for interrupting said brakingcircuit in said open position of said shutter and being closed in saidclosed position of said shutter,

a second by-pass circuit to by-pass said release switch means in saidsecond position,

second by-pass switch means arranged within said second by-pass circuit,

manually operable means for closing said second bypass switch means fora period corresponding in a maximum to the period of said open positionof said shutter.

9. The appliance, as set forth in claim 8, wherein said second by-passswitch means comprise a wiping contact switch.

10. An appliance, as set forth in claim 8, wherein said second by-passswitch means comprise,

a monostable multivibrator,

a time constant circuit to control said multivibrator and including aninterrupter, said time constant circuit having a time constantcorresponding in a maximum to the time period of said open position ofsaid shutter.

1. In a photographic film-handling appliance means defining an opticalpath, a shutter arranged on said optical path and having an openposition and a closed position, an electric motor drivingly connectedwith said shutter to control its position, a power supply circuit toenergize said motor, a braking circuit including fully electric brakemeans to stop said motor, release switch means having a first positionfor interrupting said braking circuit, and a second position forinterrupting said power supply circuit, a by-pass circuit disposed toby-pass said release switch means in said second position, by-passswitch means arranged within said by-pass circuit and operated by saidmotor, said by-pass switch means for interrupting said by-pass circuitin said closed position of said shutter and being closed in said openposition of said shutter, braking switch means arranged within saidbraking circuit and operated by said motor, said braking switch meansfor interrupting said braking circuit in said open position of saidshutter and being closed in said closed position of said shutter, saidelectric brake means for being energized only with said braking switchmeans being closed and with said release switch in said second position.2. The appliance, as set forth in claim 1, wherein Said by-pass circuitincludes a braking resistor for said motor,
 3. The appliance, as setforth in claim 1, wherein said by-pass switch means comprise aphotoelectric transducer and means for transmitting light to saidtransducer only with said shutter in open position.
 4. The appliance, asset forth in claim 1, further comprising manually operable means toclose forcibly said by-pass switch means for a period corresponding in amaximum to the period of said open position of said shutter when saidshutter is standing still in said closed position and said motor isde-energized.
 5. The appliance, as set forth in claim 4, wherein saidmanually operable means comprise means to rotate said shutter until saidby-pass switch means are closed.
 6. The appliance, as set forth in claim1, wherein said release switch means comprise a release switch and abrake control switch, said switches being operatively interconnected. 7.An appliance, as set forth in claim 6, wherein said brake control switchmeans comprises a switching transistor having an emitter-collector pathshunting said motor.
 8. In a photographic film-handling appliance meansdefining an optical path, a shutter arranged on said optical path andhaving an open position and a closed position, an electric motordrivingly connected with said shutter to control its position, a powersupply circuit to energize said motor, a braking circuit including fullyelectric brake means to stop said motor, release switch means having afirst position for interrupting said braking circuit, and a secondposition for interrupting said power supply circuit, a first by-passcircuit to by-pass said release switch means in said second position,first by-pass switch means arranged within said first by-pass circuitand operated by said motor, said first by-pass switch means forinterrupting said by-pass circuit in said closed position of saidshutter and being closed in said open position of said shutter, brakingswitch means arranged within said braking circuit and operated by saidmotor, said braking switch means for interrupting said braking circuitin said open position of said shutter and being closed in said closedposition of said shutter, a second by-pass circuit to by-pass saidrelease switch means in said second position, second by-pass switchmeans arranged within said second by-pass circuit, manually operablemeans for closing said second by-pass switch means for a periodcorresponding in a maximum to the period of said open position of saidshutter.
 9. The appliance, as set forth in claim 8, wherein said secondby-pass switch means comprise a wiping contact switch.
 10. An appliance,as set forth in claim 8, wherein said second by-pass switch meanscomprise, a monostable multivibrator, a time constant circuit to controlsaid multivibrator and including an interrupter, said time constantcircuit having a time constant corresponding in a maximum to the timeperiod of said open position of said shutter.